In recent years, electronic blackboards called interactive boards have become used that can allow letters or figures, written on a board, as such to be input in a personal computers, or conversely, image information stored in the personal computer to be projected on the board. For example, Japanese Registered Utility Model No. 3093288 (patent document 1) proposes an interactive board that can allow an image displayed on a personal computer to be projected on a board and can allow handwritten letters or images on the board to be displayed on the personal computer.
In the interactive board as proposed in the above publication, the image from the personal computer is projected from the viewer side of the board, and, thus, the interactive board is disadvantageous in that, in additionally handwriting information such as letters on the board, the projected image is blocked. Further, a space for installing a projector should be provided on the front of the board is necessary.
The above problem can be solved by projecting the image from the back surface of the interactive board (that is, a surface remote the information input surface). For example, Japanese Patent Application Laid-Open No. 276339/2003 (patent document 2) proposes an interactive board in which a projector is provided on the back surface side of the interactive board and an image is projected from the back surface of a light transparent screen. In this publication, however, the interactive board is not specifically shown as a screen that forms an image from light projected from a projector and displays the image.
A transmission screen is known that outputs video image light projected from a light source toward a viewer side to display the image. Various structures have been proposed as the transmission screen. For example, Japanese Patent Application Laid-Open No. 233154/2007 (patent document 3) proposes a transmission screen comprising a combination of a Fresnel lens with a lenticular lens. Further, Japanese Patent Application Laid-Open No. 070188/2004 (patent document 4) proposes a combination of a Fresnel lens utilizing total reflection with a light diffusing sheet for thickness reduction purposes. In these transmission screens, image light is projected from the back surface side remote from the viewer side, and, thus, a space for installing a projector is not required on the viewer side.